CD Recordable devices are made with different write, rewrite, and/or play speeds. Blaze Media Pro will automatically determine the write speed of your recordable device. However, if you are having problems (your hard drive access speed, memory, etc might not support the default speed) recording at the default speed or you want to record at a slower speed (for example you may have a 4x write speed but the CD media may only be certified for 2x) you can choose a lower speed.